The present invention relates to in situ machining of gas turbine engine components, and more particularly to in situ machining of a fan nacelle rub strip without requiring significant disassembly of the case from the engine.
A gas turbofan engine includes a high-volume fan at its forward end for forcing ambient air into a core flow passage entering an axial compressor, combustor and turbine and a fan flow passage which bypasses the core flow passage and provides direct thrust. The fan is at the forward section of the engine and is the rotating element most at risk of damage in impact with foreign objects. Damage of the fan may, in an extreme case, dislodge a fragment of the fan.
In order to contain such fragments, blade fragment containment structures typically include an annular band of a high strength material which surround the tips of the fan blades for intercepting such fragments before they can pass out of the engine. The blade fragment containment structure includes a rub strip against which the fan blade tips are closely fitted to provide a seal area which minimizes air leakage over the fan blade tips. The rub strip is manufactured of a material which may be smoothly worn away by the fan blade tips so that as tight a tip seal as possible is obtained.
During initial assembly and testing of a gas turbine engine the interface between the rub strip and the fan blade tips may not be properly configured. Furthermore, during testing the rub strip may become unevenly worn resulting in an eccentricity which may result in improper test results. In either situation, the core engine must be disassembled from the fan case and fan nacelle such that the rub strip may be replaced or machined to refine the interface or correct the eccentricity thereof. Such disassembly and reassembly may require significant time and increase the expense and complexity of engine development.
Accordingly, it is desirable to provide an efficient system and method to assure a proper fan blade tip to rub strip interface.